Cal Poly Pomona CE 222 - Notes for Chapter 11 Drainage and Drainage Structures

Unformatted text preview:

Notes for Chapter 11 Drainage and Drainage StructuresYou have to know how to use this Figure. Given two parameters, you can calculate the third one.CE222 Highway EngineeringNotes for Chapter 11 Drainage and Drainage StructuresThis chapter deals with the flow of surface water. Students should understand thefundamental concepts of highway and street drainage, factors affecting the design ofdrainage structures: shoulders, side slopes, side ditches, culverts, and bridges.1) Surface DrainageDrainage structures for surface water flow include:Pavement crownShoulderSide slopeLongitudinal ditches (channels)Culverts BridgesPavement and Shoulder Cross Slopes:Purposes are to remove surface water from wearing surface as quickly as possible.Slopes for pavement crown and shoulder can be referred to CalTrans DesignManual.Side Slopes and Side Ditches:Side ditches in cut section but not in fill sectionFlat-bottomed and V section ditchesSide ditches parallel to roadway centerlinesSide ditches provide open channels for the removal of surface water from withinthe limits of highway ROWBad design could cause erosion of soil on shoulders and side slopesProper design of curbs, gutters, and flumes as well as turf culture Culverts and Bridges: Cross-drainage structures that carry water from one side of highway to the anotherside2) Design of Surface Drainage SystemProcedures: Step 1: Runoff EstimationStep2: Identify alternative drainage systems and hydraulic designfor each drainage structure in an alternative systemStep3: Comparison of alternative systemsEach structure to be designed is a facility, just like a highway. Its design must considerthe balance of the structure’s demand and supply.Demand: Quantity of Runoff caused by rainfall.How to measure rainfall:Return period: 50-year rainfall or 30-year rainfall (which one is severe)Rainfall intensity, duration of rainfall, time of concentrationRainfall intensity-duration and return period is shown in Figure 11-2.You have to know how to use this Figure. Given two parameters, youcan calculate the third one.Demand for drainage structures is the design peak flow shown in a flood hydro-graph (see Figure 11-1).Time of Concentration (very important concept):Time of overland flow + time of flow in the drainage system (pipeline system). Time of overland flow is from the most remote point in the drainage catchment area to the inlet of the drainage system. Time of flowIn the drainage system is the flow time from intake or inlet to the point being considered.How to estimate the peak flow rate of a drainage area:The rational method: Q = CIAStudents must understand terms and concepts in the formula and beable to apply it to a drainage area with composition of different land uses.The Q estimated above represents the demand a drainage structure ( a ditch, a culvert, etc) must meet.Supply:Side ditches:Side ditches are considered as open channels. They follow Manning formula.Q = VAIf balancing the demand and supply sides of a ditch, Q can be the one estimated by the rational method.VR Sn2 3 1 2/ /Type of Open Channel Flow:Students must understand:Critical Depth- where the flow changes from tranquil to rapidCritical velocity: velocity associated with the critical depthCritical slope: slope independent of the critical depthStudent must know how to calculate critical depthStudents must understand Example 11-1 and how to use Figure 11-3. Can we use Figure 11-1 if the section is V-section.Prevention of erosion in drainage channels: Lining, that is.Culverts:Difference between a culvert and a bridge:Span < 20 ft Culvert>= 20 ft BridgeLocations of culverts: At the bottom of depressions where nonatural watercourse existsWhere natural streams intersect theroadwaysAt Locations required for passing surfacedrainage carried in side ditches beneathroads.Location Selection: right angle or a skew to roadwayAlignment and grade of culvertDesign procedures: Step 1: Site data collectionStep 2: Culvert invert elevations at inlet and outletCulvert length and slopeStep3: Determination of hearwater depth and tailwater depthStep4: Selection of type and size of culvertStep 5: Erosion protectionWhenever a culvert is placed in a natural open channel, clearly depth of theupstream water will increase. How to control the design of culvert by engineers:Culvert entrance and exit (inlet and outlet controls)Culverts flowing with Inlet control: this is for headwater.Know how to use Figure 11-6 and 11-7 for estimation of headwaterdepth given the inlet control applied.Culverts flowing with outlet control: tailwater depthCan we have culverts flowing with inlet and outlet controls at the same time?Practice indicates that there are very limited culverts with such design.Highway BridgesYou can forget them. Detailed discussion on them will be provided in othercourses.Highway Sub-drainage: forget themStudents must finish the following homework problems:11-1, 11-2, 11-4, 11-5, 11-6, and


View Full Document

Cal Poly Pomona CE 222 - Notes for Chapter 11 Drainage and Drainage Structures

Download Notes for Chapter 11 Drainage and Drainage Structures
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Notes for Chapter 11 Drainage and Drainage Structures and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Notes for Chapter 11 Drainage and Drainage Structures 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?